Having dabbled in everything from real estate to amublance driving, Kroc finally settled into a career of selling Mult-A-Mixers, machines designed to make five milkshakes simultaneously. One of his best customers was the restaurant owned by Mac (Maurice) and Dick (Richard) McDonald, where he had sold eight machines. Kroc was enamored of their standardized menu offering and assembly-line production of hamburgers (not to mention the restaurant's popularity) and in 1954 he propoosed that the brothers allow him to franchise their restaurant. Kroc sold the Mult-A-Mixer company and within six years had opened 228 McDonald's restaurants. He insisted that the franchisee run the restaurant personally, and instituted a training program to ensure that the quality of McDonald's restaurants remained consistent across stores. He bought out the McDonald brothers in 1961, and continued to run the company as president from 1955–68 and as chairman of the board from 1969–77. At the time of his death, there were 7,500 McDonald's restaurants worldwide.